The increasing complexity and density of circuitry on a printed circuit board and of components on the printed circuit board increases the difficulty of diagnosing, servicing and repairing improperly functioning printed circuit boards. Even with stringent quality control measures, circuit components have a certain probability of failure. Pretesting components increases product yield, but various circuit components are difficult to test prior to electrical connection to a printed circuit board. For example, an individual integrated circuit chip may have hundreds of closely spaced contact pads, rendering pretesting an arduous task.
One interconnection technique which permits pretesting of chips is referred to as "tape automated bonding." This fabrication procedure utilizes a continuous insulated tape which is similar to photographic film to provide a planar substrate for chips that are attached to individual sections, or frames, of the tape. A spider-like metal pattern of conductive traces is etched on each frame. The traces may either "fan out", i.e., radiate from the center of the frame to the four edges, or may consist of four sets of parallel lines, with each set extending perpendicularly from one edge of the chip. The chip is carefully aligned with the center of the frame so that the contact pads of the chip are precisely located at corresponding conductive traces in the central portion of the frame. The chip is then attached to the tape automated bonding frame. This connection of the chip contact pads to the inner portion of the frame is referred to as "inner lead bonding."
After the inner lead bonding has been performed, the integrated circuit chip may be tested. U.S. Pat. No. 4,855,672 to Shreeve teaches a method for testing the reliability of integrated circuit chips bonded to tape automated bonding frames. Prior to splicing of the continuous insulated tape into the individual lead frames having integrated circuit chips, the chips are subjected to pre-burn-in testing. The continuous insulated tape is then placed on reels and mounted within an oven. The temperature in the oven is raised to approximately 150.degree. C. and a dc bias voltage is applied to the reels to cycle each of the integrated circuit chips for a predetermined testing time. A post-burn-in test of the integrated circuit chips is then performed.
U.S. Pat. No. 4,696,526 to Newton et al. teaches that one difficulty with the reel-to-reel system of testing integrated circuit chips on a continuous insulated tape involves maintaining the burn-in temperature during testing. The Newton et al. patent teaches that high temperature testing requires that the temperature be maintained by plus or minus 1.degree. C. during the test. To overcome this problem, the prior art patent teaches use of a carrier for a tape automated bonded semiconductor device. The carrier includes alignment posts which engage sprocket holes of an individual tape automated bonding frame. The carrier provides a handling medium for pretesting of the tape automated bonding semiconductor device. The Newton et al. device is to be used with existing test equipment in the semiconductor industry.
As described in Newton et al., the test equipment used in the semiconductor industry typically includes probes which are biased to provide a contact force on the individual leads of a tape automated bonding frame. The spring-actuated probes provide the inputting and outputting of signals to the many leads of the frame. However, testing often requires repeated insertion and removal of the frame into the test equipment. For example, there may be continuity, pre-burn-in, burn-in and final-performance tests on the same frame. Each insertion of the frame jeopardizes the leads of the frame as the spring-actuated probes are pressed against the leads. Moreover, the use of the probes provide a long electrical path which is detrimental to high speed performance. A third problem is that this requirement of individually contacting the leads of the frame with spring-actuated probes limits the minimum distance between adjacent frame leads.
Some of the difficulties encountered in the use of spring-actuated probes to electrically contact leads of a tape automated bonding frame are reduced by use of manufacturing the frame with test pads at an outer periphery. The probes can then make contact with the test pads, rather than final-contact regions of the frame leads. While this signicantly reduces the likelihood of the test equipment damaging a frame lead, over a period of time the scrubbing action caused by the sideways motion of the probes will wear the probes and affect the electrical contact with the test pads. Additionally, the manufacture of tape automated bonding frames to include the test pads increases the cost of manufacture and further increases the length of a signal path during testing.
It is an object of the present invention to provide a test apparatus which includes mechanical, electrical and thermal coupling of a tape automated bonding frame and its electronic component with a reduction in signal path lengths and with an interconnection scheme which does not jeopardize the structure of the tape automated bonding frame leads.